U.S. stock index futures signaled a lower open on Monday, after stocks posted their biggest weekly decline since mid-June last week, following weaker-than-expected gross domestic product data from Japan and as investors looked for reasons to buy.

BlackBerry said its board of directors has formed a special committee to explore strategic alternatives, including going private. Shares soared more than 7 percent in pre-market trading after being temporarily halted following the news. Shares of the troubled smartphone maker have fallen nearly 20 percent this year. Its market value has fallen to $4.8 billion, from $84 billion at its peak in 2008.

"Given the importance and strength of our technology, and the evolving industry and competitive landscape, we believe that now is the right time to explore strategic alternatives," Timothy Dattels, chairman of BlackBerry's Special Committee of the Board, said in a statement.

Separately, Apple is expected to unveil its next-generation iPhone on Sept. 10 ahead of the holiday sales period. Meanwhile, rival Samsung is scheduled to take the wraps off a new Galaxy phone in Berlin, a week ahead of Apple's event, according to sources.

The Japanese Nikkei fell to a six-week low after second-quarter GDP came in at an annualized rate of 2.6 percent, lower than market forecasts of a 3.6 percent gain. However, Japanese officials said the data highlighted the success of "Abenomics", as it marked a third straight quarter of expansion.

Meanwhile, the Shanghai Composite rallied to a 7-week high after a key measure of China's money supply showed a 14.5 percent increase in July on the previous year, and new bank loans grew better than expected.

The data, released late Friday, was the latest sign of a rebound in China's economy, following last week's upbeat industrial production numbers.

Meanwhile, the U.S. Treasury will release details of its budget deficit for July at 2 p.m. ET. Plus, the Federal Reserve will purchase between $1.25 billion and $1.75 billion of 23-30 year Treasury notes.

"We look for the U.S. federal government to have posted a budget deficit of $96 billion in July, which would bring the deficit to $606 billion for the first 10 months of the fiscal year," said Barclays analysts Rahul Bajoria and Laurent Fransolet in a research note.

Among earnings, Sysco slipped after the food distributor posted earnings that fell short of expectations.